The preforms are semi-finished products made of thermoplastic material for the production of containers that are in turn obtained by means of a subsequent blow-moulding or stretch-blow moulding process. The preforms are obtained by different processes, for example by means of injection-moulding or injection-compression or extrusion moulding together with further hot-forming operations. In the production of containers made of plastic material, such as bottles for example, the preforms are typically obtained by means of injection moulding with moulds provided with a plurality of moulding cavities.
Generally, the step that is the most time-consuming of the majority of injection moulding processes is the step for cooling the moulded items. Said cooling step takes place within the mould, and more specifically within the moulding cavities, until the moulded items are sufficiently stiff to be extracted from the mould and, subsequently, handled and conveyed. It is evident that, it will not be possible to release the cavity moulds and continue the production cycle with a new moulding step, until such a time as the moulded items are sufficiently cool, and have thus solidified. Therefore, to reduce the time of an entire moulding cycle, and thus increase moulding station productivity, there have been developed several devices capable of performing at least a part of the cooling of the preforms outside of the injection mould.
The systems for removing preforms from the injection moulds are nowadays provided with a cooling circuit. Said cooling system allows the production cycle time to be reduced as already described above; indeed if the removal system is provided with a cooling system, it is possible to reduce the time that the preforms must be kept within the injection mould. These removal systems generally comprise at least one preform cooling plate that is suitable for holding and cooling the preforms originating from the mould of the injection moulding machine for a predetermined time, and this by means of the circulation of suitable fluids within the same cooling plate.
This cooling plate, also known as “post-mould device” or “take-out device” or “end-of-arm tool” (EOAT), is provided with a plurality of cooling slots, also called cups, but known as “cooling pipes”, “take-out pipes” or “cooling sleeves”.
This cooling plate is, in a first known variant, a sliding plate or take-out plate, which by translating horizontally, is inserted between the two open die halves of the injection mould. A set N of preforms, where N indicates the number of moulding cavities of the mould, is allowed to fall into the cooling slots provided on said sliding plate The sliding plate, translating once again, is extracted from the mould and placed facing an extraction device, suitable for extracting the preforms from the plate itself and for depositing them on a system suitable for the conveying thereof for packaging or for the successive blow moulding or stretch-blow moulding steps for obtaining the end containers.
Alternatively, in a second known variant, this cooling plate is a plate that rotates about an own axis of rotation, arranged outside the mould, which is suitable for receiving the set N of preforms in its cooling slots from a further sliding plate which, by translating horizontally, is inserted between the two open die halves of the injection mould to remove the set N of preforms. The additional sliding plate, translating once again, is extracted from the mould and positioned facing the rotating cooling plate. The set N of preforms is inserted into the cooling slots provided on said rotating plate. At this point, the rotating plate rotates in such a way that the face comprising the cooling slots faces an underlying extraction and conveying device that carries the preforms for packaging or to the successive blow moulding or stretch-blow moulding steps for obtaining the end containers.
In other known and more developed variants, the cooling plate can rotate about an own axis or translate thus eliminating the need to envisage a further sliding plate that removes the preforms from the injection mould.
Whatever the method and injection mould extraction device, the cooling of the moulded preforms, which began in the moulding cavities of the mould, continues and is completed in the cooling slots of the cooling plate. The cooling slots, of a more or less tubular or in any case hollow form, are affixed onto a suitable support frame or yoke, aligned in two directions of space, and arranged in rows and columns so as to form a matrix. Within each cooling slot there is obtained a seat with a geometry that reproduces the shape of the outer surface of the preform. A preform to be cooled can be inserted into each seat through an insertion opening.
Cooling fluid, e.g. water and/or air, flows through the space inside the frame and the cooling slots, in order to cool the preform inserted into said slots. A plurality of channels inside both the cooling plate and the slots allows the cooling fluid to follow a suitable path so as to lap and cool the various tubular bodies of the cooling slots.
FIG. 1 illustrates a transmission joint for a conveying and cooling apparatus for preforms belonging to the internal state of the art of the company that owns the above-mentioned patent application. Said apparatus is partially housed in a traverse carriage 1, which allows translation of the entire apparatus comprising both the cooling plate (not illustrated in FIG. 1) and a system for supplying fluids and transmitting the rotation to said cooling plate.
This system for supplying fluids and transmitting the rotation comprises (FIG. 1):                a rotating joint 2 for the distribution of fluids that performs water and air supply functions,        a water inlet pipe 3 in said rotating joint,        a water outlet pipe 4 from said rotating joint,        an air inlet pipe 5 in said rotating joint,        a mechanical support structure 6 of the rotating plate of cooling, arranged in line downstream of the rotating joint 2,        a duct 7 for the inlet of water to the inner channels of the cooling plate,        a duct 8 for recovering water from the inner channels of the cooling plate.        a duct 9 for supplying air to further inner channels of the cooling plate,        a motor 10 that is staggered with respect to the longitudinal axis defined by the rotating joint 2 and by the mechanical support structure 6,        transmission means 11 of the rotational motion, including pulleys and belt, to transmit the rotational motion from the motor 10 at one end of the mechanical support structure 6 connected to the cooling plate.        
The ducts 7, 8, 9 cross both the mechanical support structure 6 and the rotating joint 2.
Both the structure of the rotating joint for the distribution of fluids and the mechanical support structure respectively comprise a shaft and the relevant bearings.
The conveying and cooling apparatus just described, presents a number of problems.
The large number of apparatus components entails for example, a significant weight that forces limitation of the speed and acceleration performance of the traverse carriage.
The large number of components and the arrangement thereof also entails considerable overall dimensions and a complex and expensive structure.
In addition, the belt transmission means for these specific applications entail a low reliability on account of the mechanical slack, which negatively affect the necessary accuracy of position, and on account of the numerous maintenance operations, such as belt replacement, the periodic centering of belt alignment, tension checks, etc. The foregoing is thus the cause of a low repeatability of an accurate positioning.
There is therefore a need to produce a conveying and cooling apparatus for the preforms that allows the aforementioned drawbacks to be overcome.